This application relates to an improved brake system for a vehicle, particularly one which is subject to significant variable loading, such as a truck. The brake system utilizes a proportioning valve between the master cylinder and the rear brakes. Its purpose is to increase the braking effect of the rear brakes as the vehicle is loaded. Conversely, the valve decreases the rear braking effect when the vehicle load decreases.
Prior use of a rear brake proportioning valve include the 1984-1985 Chrysler Corporation built T-115 van and wagon, namely the Plymouth "Voyager" and the Dodge "Minivan" and "Caravan." In these vehicles, a proportioning valve is attached to a body cross member slightly forward of the rear axle and slightly to the left of the vehicle center line. A lever assembly is attached to the rear axle rightward of the proportioning valve and projects upward from the axle. An elongated tension-type spring extends between the lever assembly and the proportioning valve. When the vehicle is lightly loaded, the position of the lever end of the tension spring is only slightly higher than the proportioning valve end. As vehicle load increases, the valve end moves further downward with respect to the lever end and, thus, extends the spring resulting in an increased force applied to the proportioning valve. Resultantly, the valve directs increased fluid pressure to the rear brakes for greater rear braking.
The aforedescribed brake system operates satisfactorily. However, the mid-axle location of the valve, spring and lever assembly is not possible on some vehicles due to space considerations and interference with other parts. Also, this particular arrangement on the T-115 is somewhat inconvenient since the spare tire is stored immediately to the rear of these components. It would improve the accessibility of the spare tire if these brake components were located elsewhere.
It is important to place the proportioning valve where it is protected. It has been found that a desirable location for the valve is just forward of the rear wheel and up near the forward end portion of the rear leaf-type suspension spring. This is where the forward end of the leaf spring is pivotally connected to the vehicle. In this location, the proportioning valve can be supported by the same longitudinal body or chassis member which also supports the spring end. The input device for the valve which senses vehicle loading and includes a suspension spring position sensing means is directly responsive to movements of the leaf spring end.
The extent of vehicle load in the subject application is sensed by a position follower device which is operably connected to the forward end portion of the rear suspension spring. As the vehicle load increases, the spring's end portion is pivoted through an arc as the vehicle body and attached spring portion move downward with respect to the spring mid-portion. A position follower member for the end portion of the spring includes an elongated lever means which is supported for pivotal movement at a mid-location and about an axis generally parallel to the axis about which the spring end portion pivots in response to load changes. The more rearward portion of the follower extends past the pivotal support of the spring and overlies the spring end. A contact device on the end of the rearwardly extending portion rests against the top surface of the spring and generates angular pivoting of the lever means about its midpoint mount. The forward portion of the follower lever is normally directed slightly downward from the horizontal. As the vehicle load is increased, the follower lever pivots to move the forward end further downward.
A spring-like and axial connector extends from the forward end of the follower lever to the input control of the proportioning valve which is force responsive. As the follower pivots due to loading of the vehicle, the force input to the proportioning valve is increased by extension of the spring connector. Resultantly, an increased brake pressure is directed to the rear brakes.
The spring contact device on the end of the follower lever is held against the upper surface of the spring by means of a yieldable bias control device. This device includes a molded rubber bumper-like member with a hollowed mid-portion which is positioned next to the follower lever's pivot and slightly rearwardly toward the spring contact device. As vehicle loading is increased, the suspension spring causes the pivoting of the lever against the hollow bumper member. Resultant yieldable distortion of the bumper into a more flattened configuration produces a return bias on the lever. When the load is decreased, the bumper and spring-like connector cooperate to pivot the lever and contact device against the suspension spring.
Therefore, an object of the invention is to provide an improved vehicle brake proportioning system which utilizes a vehicle load sensing means operating directly in response to movements of a vehicle rear suspension spring for controlling an input of a proportioning valve in the fluid circuit of the brake system.
A further object of the invention is to provide an improved vehicle brake proportioning system which utilizes a vehicle load sensing means operating directly in response to movements of the end portion of the rear suspension spring so as to pivot along with the end of the spring as it responds to increased vehicle loading and transmits load inputs via an axially yieldable, spring-like connector to the proportioning valve.
Other objects and advantages of the subject invention will be readily apparent from a reading of the following detailed description of the preferred embodiment, which is shown in the following drawings.